Research Article Small Size and Low Cost UHF RFID Tag ...
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Research Article Small Size and Low Cost UHF RFID Tag Antenna Mountable on Metallic Objects Sergio López-Soriano and Josep Parrón Department of Telecommunication and System Engineering, Escola T` ecnica Superior d’Enginyeria (ETSE), Universitat Aut` onoma de Barcelona (UAB), Campus de la UAB, Q Building, Carrer de les Sitges, Bellaterra, Cerdanyola del Vall` es, 08193 Barcelona, Spain Correspondence should be addressed to Sergio L´ opez-Soriano; [email protected] Received 23 July 2015; Revised 9 October 2015; Accepted 12 October 2015 Academic Editor: Ahmed A. Kishk Copyright © 2015 S. L´ opez-Soriano and J. Parr´ on. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Reducing tag size while maintaining good performance is one of the major challenges in radio-frequency identification applications (RFID), in particular when labeling metallic objects. In this contribution, a small size and low cost tag antenna for identifying metal objects in the European UHF band (865–868 MHz) is presented. e antenna consists of a transmission line mounted on an inexpensive thin dielectric which is proximity-coupled to a short-ended patch mounted on FR4 substrate. e overall dimensions of the tag are 33.5 × 30 × 3.1 mm. Experimental results show that, for an EIRP of 3.2 W (European regulations), such a small and cheap tag attains read ranges of about 5 m when attached to a metallic object. 1. Introduction To date, research efforts in the design of UHF RFID tag antennas have been directed toward the following issues: (i) reducing the overall size, (ii) lowering the fabrication costs, and (iii) achieving the specifications of a particular application. In particular, metal-mountable tags have the challenge of achieving read ranges of a few meters with small size and low cost [1]. In the literature, we find several solutions for metal- mountable applications: antennas integrating EBG structures [2], antennas using high permittivity materials [3–5], and antennas based on microstrip patch concepts [6–10]. From the viewpoint of cost and manufacturing complexity, this latter group provides the best solution since such designs frequently make use of low cost FR4 dielectric substrate ( 1 = 4.2, tan = 0.02, and thickness of 3 mm) [6–9]. e area and read range of typical tags are summarized in Table 1. As might be expected, there is a tradeoff between the area occupied and the read range. We can also see that tags occupying similar area may produce very different read ranges. erefore, the antenna configuration can make a difference in the tag performance. In this paper we propose an antenna configuration that comprises a fixed part that determines the behavior of the antenna in terms of radiation and a variable part that can be used to easily match the antenna to the wide variety of integrated circuits (ICs) that can be found in the market. We will show how this configuration can be implemented with low cost materials, resulting in a tag of small size and good performance when placed on metal surfaces. 2. Antenna Design e proposed antenna is illustrated in Figure 1. e patch, which is mounted on FR4 substrate, is designed to operate in a given band and can remain unchanged for different ICs. It has been short-ended in order to reduce the size [11]. Moreover, a slot has been cut in the patch with a view to obtain additional size reduction. e patch is proximity-coupled to a transmission line which is mounted on an inexpensive thin dielectric. Adjust- ing the dimensions of the transmission line will slightly modify the input impedance of the antenna, thus making it possible to match it to a particular IC impedance. Hindawi Publishing Corporation International Journal of Antennas and Propagation Volume 2015, Article ID 870478, 6 pages http://dx.doi.org/10.1155/2015/870478
Transcript of Research Article Small Size and Low Cost UHF RFID Tag ...
Research ArticleSmall Size and Low Cost UHF RFID Tag Antenna Mountable onMetallic Objects
Sergio López-Soriano and Josep Parrón
Department of Telecommunication and System Engineering, Escola Tecnica Superior d’Enginyeria (ETSE),Universitat Autonoma de Barcelona (UAB), Campus de la UAB, Q Building, Carrer de les Sitges, Bellaterra,Cerdanyola del Valles, 08193 Barcelona, Spain
Correspondence should be addressed to Sergio Lopez-Soriano; [email protected]
Received 23 July 2015; Revised 9 October 2015; Accepted 12 October 2015
Academic Editor: Ahmed A. Kishk
Copyright © 2015 S. Lopez-Soriano and J. Parron. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.
Reducing tag size whilemaintaining good performance is one of themajor challenges in radio-frequency identification applications(RFID), in particular when labeling metallic objects. In this contribution, a small size and low cost tag antenna for identifyingmetal objects in the European UHF band (865–868MHz) is presented. The antenna consists of a transmission line mounted on aninexpensive thin dielectric which is proximity-coupled to a short-ended patch mounted on FR4 substrate. The overall dimensionsof the tag are 33.5 × 30 × 3.1mm. Experimental results show that, for an EIRP of 3.2W (European regulations), such a small andcheap tag attains read ranges of about 5m when attached to a metallic object.
1. Introduction
To date, research efforts in the design of UHF RFID tagantennas have been directed toward the following issues:(i) reducing the overall size, (ii) lowering the fabricationcosts, and (iii) achieving the specifications of a particularapplication. In particular, metal-mountable tags have thechallenge of achieving read ranges of a few meters with smallsize and low cost [1].
In the literature, we find several solutions for metal-mountable applications: antennas integrating EBG structures[2], antennas using high permittivity materials [3–5], andantennas based on microstrip patch concepts [6–10]. Fromthe viewpoint of cost and manufacturing complexity, thislatter group provides the best solution since such designsfrequentlymake use of low cost FR4 dielectric substrate (𝜀
𝑟1=
4.2, tan 𝛿 = 0.02, and thickness of 3mm) [6–9]. The area andread range of typical tags are summarized in Table 1.
As might be expected, there is a tradeoff between thearea occupied and the read range. We can also see thattags occupying similar area may produce very different readranges. Therefore, the antenna configuration can make adifference in the tag performance.
In this paper we propose an antenna configuration thatcomprises a fixed part that determines the behavior of theantenna in terms of radiation and a variable part that canbe used to easily match the antenna to the wide variety ofintegrated circuits (ICs) that can be found in the market. Wewill show how this configuration can be implemented withlow cost materials, resulting in a tag of small size and goodperformance when placed on metal surfaces.
2. Antenna Design
The proposed antenna is illustrated in Figure 1. The patch,which ismounted onFR4 substrate, is designed to operate in agiven band and can remain unchanged for different ICs. It hasbeen short-ended in order to reduce the size [11]. Moreover, aslot has been cut in the patch with a view to obtain additionalsize reduction.
The patch is proximity-coupled to a transmission linewhich is mounted on an inexpensive thin dielectric. Adjust-ing the dimensions of the transmission line will slightlymodify the input impedance of the antenna, thus making itpossible to match it to a particular IC impedance.
Hindawi Publishing CorporationInternational Journal of Antennas and PropagationVolume 2015, Article ID 870478, 6 pageshttp://dx.doi.org/10.1155/2015/870478
2 International Journal of Antennas and Propagation
Open circuit
Slot
GroundShorted end
Patch Transmission line IC
Paper
Dielectric(FR4)
x
y
z
Figure 1: Antenna geometry.
Table 1: Size and read range for different metal tags that can befound in literature (EIRP: 4W).
Reference Area (mm2) Read range (m)[6] 32 × 18 1.5[7] 53 × 20 2.5[8] 55 × 22 4.7[9] 68 × 30 9.5
Table 2: Prototype dimensions (in mm).
𝐿 𝐿𝑝𝐿 tl 𝐿 𝑠1 𝐿 𝑠2 𝑔 𝑊 𝑊tl 𝑊𝑠 ℎ1 ℎ2
33.5 30.5 33.5 1 1 3 30 1 28 3.1 0.1
The parameters involved in the design are illustratedin Figure 2. A thickness of 3mm (ℎ
1) has been selected
for the patch substrate for comparison purposes. Regardingthe transmission line, it consists of a copper strip whichis separated from the patch by a standard paper sheet ofthickness 100 𝜇m (𝜀
𝑟2= 3.85 and tan 𝛿 = 0.08 [7]).
The tag has been designed over an infinite ground planeusing the simulation software FEKO [12]. The antenna ismatched to work with the Alien Higgs-3 integrated circuit[13] (30 − 𝑗211Ω at 867MHz). Therefore, to obtain themaximum power transfer between the antenna and the ICcomplex conjugate impedance matching is required. Table 2summarizes the final dimensions of the tag.
3. Parametric Study
In order to justify the election of the final dimensions ofthe prototype a study on the effects of the main designparameters has been conducted with FEKO to provide abetter understanding of the antenna operation. The valuesin Table 2 will be used as reference dimensions for allsimulations. All gain results are given for the 𝑧-axis direction.
3.1. Radiating Patch. The length of the patch (𝐿𝑝) controls the
resonant frequency of the antenna that roughly correspondsto a quarter of the effective wavelength (Figure 3). It is tunedto provide the inductance that compensates the chip capaci-tance at the operation frequency. As previously commented, a
Lpg
Ls2
Ls1
W
Ws
h2
h1
L
L tl
Wtl
Figure 2: Antenna geometric parameters (top and front view).
slot is cut on the patch thereby increasing its electrical length.This effect is illustrated in Figure 4.
The gap (𝑔), the width (𝑊), and the substrate thickness(ℎ1) also affect the input impedance of the antenna but we use
them to optimize the antenna gain since they also determinethe size of the radiating slot of the patch. Figure 5 showsthat the thickness is the most relevant parameter for the gainwhereas a fine tuning of the gap size (Figure 6) and the width(Figure 7) can provide additional dBs of improvement.
3.2. Feeding Transmission Line. Once the patch has beenadjusted to achieve the maximum gain in the desired band,the designer can use the width (𝑊tl), length (𝐿 tl), andthickness (ℎ
2) of the transmission line to match the reactance
of different integrated circuits without modifying signifi-cantly the gain. Figure 8 shows the range of variation thatcan be achieved in the input impedance by changing thelength whereas Figure 9 shows that the thickness controls the
International Journal of Antennas and Propagation 3
Resistance
Reactance
1000
500
−500
800 850 900 950 1000
Frequency (MHz)
Impe
danc
e (Ω
)
Lp = 29.5mmLp = 30.5mmLp = 32mm
0
Figure 3: Antenna input impedance for different lengths of thepatch.
1000
500
0
−500
Impe
danc
e (Ω
)
Frequency (MHz)800 850 900 950 1000
Ws = 26mmWs = 27mmWs = 28mm
Figure 4: Antenna input impedance for different widths of the slot.
coupling between the transmission line and the patch andprovides an extra parameter to match the antenna to the IC.
4. Simulation and Experimental Results
The fabricated prototype is shown in Figure 10. The IC iseasily soldered over the copper strip.
The impedance measurements are conducted over aground plane of 1 × 1m2. Themeasurement setup is shown inFigure 11.The setup is calibrated at the end of the SMAcoaxialcable, and then, an electrical delay of 1.46 ns is added in orderto take into account the effect of theMMCX cable, which waspreviously characterized.
Frequency (MHz)800 850 900 950 1000
h1 = 0.8mmh1 = 1.55mmh1 = 3.1mm
−50
−45
−40
−35
−30
−25
−20
−15
−10
−5
Gai
n (d
B)
Figure 5: Antenna gain for different thicknesses of the patch.
Frequency (MHz)800 850 900 950 1000
g = 1mmg = 2mmg = 3mm
−10.5
−10.0
−9.5
−9.0
−8.5
−8.0
−7.5G
ain
(dB)
Figure 6: Antenna gain for different sizes of the gap.
Measurements have proven to be repeatable. The mea-sured and simulated input impedance are compared inFigure 12. Despite the slight displacement of the measuredreactance, both results are in good agreement.
Figure 13 depicts the simulated radiation pattern of theprototype antenna over a 20 × 20 cm2 metal plate. Asexpected, it is similar to a slot oriented along the 𝑦-axis ina finite ground plane. The maximum gain is −6 dB in the +𝑧direction.
The read range measurements have been carried outusing the Impinj Speedway Revolution R220 reader [14]and the antenna S8658P from Laird Technologies [15]. Themeasurement setup is shown in Figure 14.
Although the EIRP for the European standard is 3.2W,the EIRP was set up to be 4W (American standard) in
4 International Journal of Antennas and Propagation
Frequency (MHz)800 850 900 950 1000
W = 25mmW = 30mmW = 35mm
−7
−8
−9
−10
−11
−12
−13
Gai
n (d
B)
Figure 7: Antenna gain for different widths of the patch.
1000
500
0
−500
Impe
danc
e (Ω
)
Frequency (MHz)800 850 900 950 1000
L tl = 31.5mmL tl = 32.5mmL tl = 33.5mm
Figure 8: Antenna input impedance for different lengths of thetransmission line.
order to compare with Table 1. Measurements show that ourprototype, placed on top of a 20× 20 cm2metal plate, achievesa read range of 5.6m; therefore, it improves substantially theread range of some low cost tags that occupy approximatelythe same area.
The Voyantic Tagformance equipment [16] has also beenused to evaluate the read range of our tag with respect tofrequency. In this case, the tag has been placed over ametallicbox of 15 × 8 × 6 cm2. This box modifies slightly the tagperformance with respect to 20 × 20 cm2 metal plate, sincethe gain is about 1 dB smaller and the peak of read range isshifted toward upper frequencies (Figure 15).
1000
500
0
−500
Impe
danc
e (Ω
)
Frequency (MHz)800 850 900 950 1000
h2 = 0.1mmh2 = 0.2mmh2 = 0.5mm
Figure 9: Antenna input impedance for different thicknesses of thetransmission line.
IC
Pad
Figure 10: Fabricated prototype.
MMCX cable
SMA cableAntenna
VNA
Figure 11: Impedance measurement setup.
5. Conclusions
The RFID tag presented in this paper is highly suitable foridentification of metallic objects and is based on a transmis-sion line that is proximity-coupled to a short-ended patch.The parametric study carried out shows that the radiating
International Journal of Antennas and Propagation 5
1000
500
0
−500
Impe
danc
e (Ω
)
Frequency (MHz)800 850 900 950 1000
Sim(Re(Zin))Sim(Im(Zin))Fab(Re(Zin))
Fab(Im(Zin))Re(ZIC)−Im(ZIC)
Figure 12: Simulated (blue) and measured (green) antenna’s inputimpedance and IC’s impedance (red).
X
Y
Z−6.0
−8.0
−10.0
−12.0
−14.0
−16.0
−18.0
−20.0
−22.0
−24.0
−26.0
Tota
l gai
n (d
Bi)
Figure 13: Simulated radiation pattern for a 20× 20 cm2metal plate.
Tag
metal plate
RFID reader
Reader antenna
20 × 20 cm2
Figure 14: Read range measurement setup.
patch can be optimized to achieve the maximum gain in thedesired bandwhile the feeding transmission line can be easilytuned to match different integrated circuits.
The proposed tag has beenmade of inexpensive materialswith a simple and repeatable procedure and has dimensionsof 33.5 × 30 × 3.1mm.The read range of the tag has proven tobe significantly better than other solutions that can be foundin literature with approximately the same area [7, 8].
Frequency (MHz)8000
1
2
3
4
5
825 850 875 900 920
Read
rang
e (m
)
Figure 15: Voyantic read range measurement.
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper.
Acknowledgments
This work was supported by the Universitat Autonoma deBarcelona and the Spanish Ministry of Economy and Com-petitiveness through Project TEC2012-37582-C04-01 andFEDER funds.
References
[1] T. Bjorninen, L. Sydanheimo, L. Ukkonen, and Y. Rahmat-Samii, “Advances in antenna designs forUHFRFID tagsmount-able on conductive items,” IEEE Antennas and PropagationMagazine, vol. 56, no. 1, pp. 79–103, 2014.
[2] B. Gao and M. M. F. Yuen, “Passive UHF RFID packaging withelectromagnetic band gap (EBG) material for metallic objectstracking,” IEEE Transactions on Components, Packaging andManufacturing Technology, vol. 1, no. 8, pp. 1140–1146, 2011.
[3] A. A. Babar, T. Bjorninen, V. A. Bhagavati, L. Sydanheimo, P.Kallio, and L. Ukkonen, “Small and flexible metal mountablepassive UHF RFID tag on high-dielectric polymer-ceramiccomposite substrate,” IEEE Antennas and Wireless PropagationLetters, vol. 11, pp. 1319–1322, 2012.
[4] A. A. Babar, J. Virtanen, V. A. Bhagavati et al., “Inkjet-printable UHF RFID tag antenna on a flexible ceramic-polymercomposite substrate,” in Proceedings of the IEEEMTT-S Interna-tional Microwave Symposium Digest (MTT ’12), pp. 1–3, IEEE,Montreal, Canada, June 2012.
[5] J.-S. Kim,W.-K. Choi, andG.-Y. Choi, “Small proximity coupledceramic patch antenna for UHF RFID tag mountable onmetallic objects,” Progress in Electromagnetic Research C, vol. 4,pp. 129–138, 2008.
[6] S.-L. Chen, “A miniature RFID tag antenna design for metallicobjects application,” IEEE Antennas and Wireless PropagationLetters, vol. 8, pp. 1043–1045, 2009.
[7] P. H. Yang, Y. Li, L. Jiang, W. C. Chew, and T. T. Ye, “Compactmetallic RFID tag antennas with a loop-fed method,” IEEE
6 International Journal of Antennas and Propagation
Transactions on Antennas and Propagation, vol. 59, no. 12, pp.4454–4462, 2011.
[8] L. Mo and C. Qin, “Tunable compact UHF RFID metal tagbased on CPW open stub feed PIFA antenna,” InternationalJournal of Antennas and Propagation, vol. 2012, Article ID167658, 8 pages, 2012.
[9] K.-H. Lin, S.-L. Chen, and R. Mittra, “A looped-bowtie RFIDtag antenna design for metallic objects,” IEEE Transactions onAntennas and Propagation, vol. 61, no. 2, pp. 499–505, 2013.
[10] Xerafy: Mercury Metal Skin Inlay, http://www.xerafy.com/catalogue/product/metal-skin-inlay/1.
[11] P. Mirchandani, K. Deshpande, and R. Khan, “Performanceanalysis of miniaturized microstrip patch antennas for UHFRFID applications,” in Proceedings of the International Con-ference on Signal Processing, Communication, Computing andNetworking Technologies (ICSCCN ’11), pp. 244–249, IEEE,Thuckalay, India, July 2011.
[12] FEKO EM Simulation software, http://www.feko.info.[13] Alien Technology Corporation, Higgs-3 product brief, http://
www.alinetechnology.com/ic/higgs-3.[14] Impinj, Speedway Revolution R220, http://www.impinj.com/
products/speedway/speedway-revolution-rfid-readers/.[15] Laird Technologies, S8658P, http://www.lairdtech.com/pro-
ducts/s8658pr.[16] Voyantic Tagformance, https://voyantic.com/tagformance.
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